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3.0 SITE INVESTIGATION RESULTS <br /> 31 Geology and Hydrogeology <br /> Based on the drilling of the four groundwater table monitoring wells and four CPT soil borings, <br /> subsurface soils generally consist of discontinuous sand and silty sand intervals interbedded with <br /> ' finer-grained soils to a depth of approximately 65 feet Between 65 and 90 feet, more massive <br /> sand and gravel intervals are continuous across the site The general distribution of subsurface <br /> soils is shown in cross-section (Figure 3) Detailed soil descriptions are included in the CPT <br /> report (Appendix B) and on the monitoring well logs (Appendix D) <br /> Based on the CPT and pore pressure dissipation data, groundwater-bearing zones were identified <br /> beneath the groundwater table In CPT-2 and CPT-3, a groundwater zone was identified at <br /> approximately 57-58 feet bgs In CPT-4, a groundwater zone was identified at approximately 66 <br /> feet bgs At all four CPT locations, a deeper groundwater-bearing zone was also identified at <br /> approximately 77-78 feet <br /> On September 25, 2000, the static depth to the groundwater table, as measured in the four <br /> groundwater monitoring wells, ranged from 20 69 feet bgs in MW-1 to 21 79 feet bgs in MW-2 <br /> lieThe corresponding groundwater surface elevation ranged from a high of 16 83 feet above mean <br /> sea level (msl) at MW-1 to a low of 16 17 feet msl at MW-4 The resulting groundwater surface <br /> appears as a plane dipping to the northeast at a gradient of approximately 0 00825 foot/foot A <br /> groundwater surface contour map is included as Figure 4 The well construction details, wellhead <br /> elevations and groundwater monitoring data are summarized in Table 4 <br /> 32 Analytical Results <br /> ' In the seven soil samples collected using the CPT rig, only the samples from 40 and 50 feet from <br /> ' CPT-4 contained detectable concentrations of gasoline constituent compounds The sample <br /> collected at 40 feet only contained 0 0089 mg/kg of MTBE, and the sample collected at 50 feet <br /> only contained 0 04 mg/kg of MTBE No other gasoline constituent compound was detected <br /> These sod sample results are summarized in Table 5 The laboratory report is included in <br /> Appendix F <br /> 13 <br />